1. Field of the Invention
The present invention relates to a seal apparatus for sealing dampening solution. More specifically, the present invention relates to a seal apparatus for sealing dampening solution which is disposed within a reservoir extending from a nip defined between a form roller and a metering roller of a lithographic printing machine.
2. Information Disclosure Statement
In the lithographic printing art, a form roller and a metering roller are positioned such that the form roller is urged against the metering roller to form a nip therebetween. The form roller includes a cover which may be of rubber. The metering roller also has a cover. The wedge shaped space above the form and metering rollers is filled with dampening solution by means of a constant level filling arrangement. As the form and metering rollers rotate, dampening solution is metered by the nip and is transferred from the surface of the cover of the form roller to a lithographic printing plate secured around the periphery of a rotating plate cylinder. Subsequent to the application of dampening solution to the printing plate, ink is applied to the dampened surface of the printing plate by means of a train of inking rollers which cooperate with an ink fountain. Consequently, due to the prior treatment of the plate, certain portions of the surface of the printing plate will be receptive to the transfer thereto of damping solution and subsequently to the reception of ink. However, other portions of the surface of the plate will be non receptive to such dampening solution and will not therefore take up any dampening solution or any ink. Such hydrophobic portions of the surface of the plate will therefore be devoid of ink. Furthermore, the hydrophilic portions of the surface of the printing plate will be receptive first to the dampening solution and then to the printing ink. Due to the rotation of the plate cylinder, the ink image formed on the plate will be transferred to the surface of a blanket secured to the periphery of a rotating blanket cylinder. As the blanket cylinder rotates, the ink image on the surface of the blanket is transferred to a web of paper extending through a nip defined between the blanket cylinder and a backing roller.
As the form and metering rollers are rotating, dampening solution is transferred by the form roller and is applied to the printing plate secured to the plate cylinder. However, during continued rotation of the form roller in contact with the printing plate, ink particles subsequently applied to the dampened plate will be taken up by the form roller from the printing plate. Such ink particles will mix with the dampening solution. Consequently, during prolonged usage of the printing machine, if such mixture of ink and dampening solution were to leak past the edges of the reservoir, such leakage could spoil an image subsequently transferred to the paper web.
The present invention relates to the provision of air dam seals disposed at the edges of the reservoir for preventing leakage of dampening solution and ink particles.
Therefore, it is a primary feature of the present invention, to provide air dam seals disposed at the edges of a reservoir that overcomes the problems associated with the prior art devices and which make a considerable contribution to the art of lithographic printing.
Another feature of the present invention is the provision of air dam seals which prevent leakage past the edges of a reservoir.
A further feature of the present invention is the provision of air dam seals which permits prolonged usage of the printing setup without marring the quality of the printed product.
Other features and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained herein with reference to the annexed drawings which show a preferred embodiment of the present invention.
The present invention relates to a seal apparatus for sealing dampening solution which is disposed within a reservoir extending from a nip defined between a form roller and a metering roller of a lithographic printing machine. The apparatus includes a conduit having a first and a second end, the first end being connected to a source of pressurized air. A nozzle is sealingly connected to the second end of the conduit, the nozzle being located adjacent to an edge of the reservoir. The arrangement is structured such that in use of the apparatus, pressurized air flows from the source of pressurized air through the conduit to the nozzle so that the nozzle directs a flow of air towards the edge of the reservoir and between the form and metering rollers such that the flow of air generates an air dam for sealing the reservoir so that leakage of the dampening solution from the edge of the reservoir is inhibited.
In a more specific embodiment of the present invention, the conduit includes a plastic tube and the plastic tube is flexible.
Also, the nozzle defines a throat which increases the velocity of the flow of air so that the flow of air reliably and predictably impedes leakage of the dampening solution from the edge of the reservoir.
The apparatus further includes a further conduit having a first and a second extremity, the first extremity being connected to the source of pressurized air. A further nozzle is sealingly connected to the second extremity of the further conduit, the further nozzle being located adjacent to a further edge of the reservoir. The further edge of the reservoir is disposed between the form and metering rollers and is spaced axially along the rollers relative to the edge. The arrangement is structured such that in use of the apparatus, pressurized air flows from the source of pressurized air through the conduit to the nozzle so that the nozzle directs a flow of air towards the edge of the reservoir and between the form and metering rollers such that the flow of air generates an air dam for sealing the reservoir so that leakage of the dampening solution from the edge of the reservoir is inhibited.
Additionally, the arrangement is such that pressurized air also flows from the source of pressurized air through the further conduit to the further nozzle so that the further nozzle directs a further flow of air towards the further edge of the reservoir and between the form and metering rollers such that the further flow of air generates a further air dam for sealing the reservoir so that leakage of the dampening solution from the further edge of the reservoir is inhibited.
In another embodiment of the present invention, a wedge shaped seal is disposed between the nozzle and the edge of the reservoir for assisting in the generation of the air dam, the wedge shaped seal diverting the flow of air so that the flow of air flows towards a periphery defined by the wedge shaped seal so that leakage of dampening solution from the reservoir past the periphery of the wedge shaped seal is prevented.
Furthermore, the wedge shaped seal is of cusp shaped configuration, the wedge shaped seal having a point and a first and a second curved surface. The arrangement is such that the point is disposed closely adjacent to the nip defined between the form and metering rollers, the first curved surface being disposed in spaced close proximity to the form roller and the second curved surface is disposed in spaced close proximity to the metering roller.
More specifically, in a preferred embodiment, the wedge shaped seal is fabricated from a plastics material and is adjustably disposed relative to the edge of the reservoir.
Moreover, the wedge shaped seal is disposed spaced from the form and metering rollers so that friction and wear between the wedge shaped seal and adjacent rollers is inhibited.
The wedge shaped seal is disposed between the nozzle and the edge of the reservoir for assisting in the generation of the air dam, the wedge shaped seal diverting the flow of air so that the flow of air flows towards a periphery defined by the wedge shaped seal so that leakage of the dampening solution from the reservoir past the periphery of the wedge shaped seal is prevented. Also, a further wedge shaped seal is disposed between the further nozzle and the further edge of the reservoir for assisting in the generation of the further air dam. The further wedge shaped seal diverts the further flow of air so that the further flow of air flows towards a further periphery defined by the further wedge shaped seal so that leakage of the dampening solution from the reservoir past the further periphery of the further wedge shaped seal is prevented.
The further wedge shaped seal is of cusp shaped configuration, the further wedge shaped seal having a further point and a further first and a second curved surface. The arrangement is such that the further point is disposed closely adjacent to the nip defined between the form and metering rollers. The further first curved surface is disposed in spaced close proximity to the form roller while the further second curved surface is disposed in spaced close proximity to the metering roller.
In a preferred embodiment of the present invention, the further wedge shaped seal is fabricated from a plastics material and is adjustably disposed relative to the further edge of the reservoir.
Also, the further wedge shaped seal is disposed spaced from the form and metering rollers so that friction and wear between the further wedge shaped seal and the adjacent rollers is inhibited.
Many modifications and variations of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter. However, such modifications and variations fall within the spirit and scope of the present invention as defined by the appended claims.